1. Field Of The Invention
This invention relates to a seal to assure an air tight laser optical path, and more particularly, a rolling diaphragm type seal used in connection with a laser control for an aspheric generator.
2. Description Of The Prior Art
An aspheric generator, such as that manufactured by the Moore Special Tool Co., Inc. of Bridgeport, Conn., is a three-axes computer numerically controlled precision maching apparatus designed to produce microinch finishes on a broad spectrum of materials. The apparatus can be used for single point diamond turning or for grinding. This dual capability allows a machinist to not only produce mirror quality finishes, but also to grind molds to crucial tolerances for optical lenses, and to handle other grinding tasks related to precision machining. In its diamond turning mode, the state of the art aspheric generator can produce finished optics on the machine and can be used for the production of discs used in the computer and photocopier fields. In its grinding mode, the aspheric generator can grind to tolerances of twenty millions of an inch (0.5.mu.m) or better. This enables it to produce glass optical elements--spheres and aspheres--in most cases ready to polish, and ceramics for use as injection molding dyes which are used to produce plastic lenses.
High precision tolerances and resolution are achieved by the use of a laser feedback system to control the movement of the beds of the aspheric generator apparatus along the various axes, such as the X and Z linear axes of the apparatus. The laser feedback system is operated by a suitable computer program which outlines the work to be performed on the work piece held in the chuck of the machine.
The laser beams which control movement of the beds of the apparatus, which in turn produce the required movement of the tool against the work piece, which movement can be measured in microinches to produce the high quality finishes which are required, are generated and enclosed in telescoping tubes which also house a reflective mirror, an interferometer and a receiver to monitor the displacement; and through a comparison interferometer network, to cause movement of one of the two tubes provided on a linear axis, such as the X or Z axis to achieve the required motion of the bed and tool along that axis. The tubes are connected to the appropriate tool bed axis to develop the required movement.
The laser optical path in the laser feedback system tubes must be airtight. The humidity within the tubes must be controlled and lubricants must be precluded from impinging on the various mirror or interferometer surfaces within the tubes. In the former instance, a change in the density of the atmosphere within the tubes will effect the intensity of the laser beam and its reflective quality causing error in the movement of the tool. In the latter instance, if dirt or grease impinge upon any of the mirror surfaces, the apparatus must be cleaned and taken apart, resulting in considerable down time. Accordingly, a suitable seal between the telescoping tubes and the ambient environment must be maintained to preclude lubricant and dirt from entering the interior of the tubes and the density of the atmosphere within the tubes from being changed during operation of the apparatus.
Heretofore it has been common to use rolling diaphragm seals between telescoping parts, such as a piston and cylinder. As disclosed in the June 19, 1969 issue of "Machine Designing", as a piston moves in a cylinder, a rubber seal or sleeve connected between the cylinder and the piston will roll off the piston side wall onto the cylinder side wall. This effectively seals the space in the cylinder above the piston. The diaphragm consists of a single wall sleeve or tube having one end fixed to the cylinder and the end fixed to the piston and as indicated, rolls between the two elements as the piston travels linearly in the cylinder. However, where the length of travel of the telescoping parts is considerable, the ends of such a seal tend to frictionally roll against each other during the linear travel of the parts creating considerable drag or friction and resistance to movement. Where accuracy of movement in the millions of an inch category are required, as for example in an aspheric generator, such seals cannot be used because of the tendency of the material to drag against itself at its ends thereby impeding accurate movement. The same would be true of 0-ring seals and bellow-type seals, the latter being impeded by undue air friction in its expansion and contraction.
Accordingly, it is the primary object to this invention to provide an effective seal between a pair of telescoping tubes housing various laser components of a laser feedback system for an aspheric generator.
It is a further object of this invention to provide a seal of the type indicated which provides minimal frictional impedence of resistance to movement of the telescoping tubes housing the laser feedback components.